Dynamic stabilization connecting member with slitted core and outer sleeve

ABSTRACT

A dynamic fixation medical implant having at least two bone anchors includes a longitudinal connecting member assembly having an elongate core and an outer sleeve. The core may be substantially cylindrical, of one-piece construction, and includes end portions for attachment to the bone anchors. A portion of the core extending between the bone anchors has at least one slit. The outer sleeve may include compression grooves. The sleeve surrounds the core and extends between the pair of bone anchors, the sleeve being compressible in a longitudinal direction between the bone anchors.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/850,464 filed Oct. 10, 2006, the disclosure of which is incorporatedby reference herein. This application is also a continuation-in-part ofU.S. patent application Ser. No. 11/522,503, filed Sep. 14, 2006 thatclaims the benefit of U.S. Provisional Application Nos. 60/722,300,filed Sep. 30, 2005; 60/725,445, filed Oct. 11, 2005; 60/728,912, filedOct. 21, 2005; 60/736,112, filed Nov. 10, 2005, and 60/832,644, filedJul. 21, 2006; the disclosures all of which are incorporated byreference herein.

BACKGROUND OF THE INVENTION

The present invention is directed to dynamic fixation assemblies for usein bone surgery, particularly spinal surgery, and in particular tolongitudinal connecting members and cooperating bone anchors orfasteners for such assemblies, the connecting members being attached toat least two bone fasteners.

Historically, it has been common to fuse adjacent vertebrae that areplaced in fixed relation by the installation therealong of bone screwsor other bone anchors and cooperating longitudinal connecting members orother elongate members. Fusion results in the permanent immobilizationof one or more of the intervertebral joints. Because the anchoring ofbone screws, hooks and other types of anchors directly to a vertebra canresult in significant forces being placed on the vertebra, and suchforces may ultimately result in the loosening of the bone screw or otheranchor from the vertebra, fusion allows for the growth and developmentof a bone counterpart to the longitudinal connecting member that canmaintain the spine in the desired position even if the implantsultimately fail or are removed. Because fusion has been a desiredcomponent of spinal stabilization procedures, longitudinal connectingmembers have been designed that are of a material, size and shape tolargely resist flexure, extension, torsion, distraction and compression,and thus substantially immobilize the portion of the spine that is to befused. Thus, longitudinal connecting members are typically uniform alongan entire length thereof, and usually made from a single or integralpiece of material having a uniform diameter, width or cross-sectionalarea of a size to provide substantially rigid support in all planes withvarying degrees of rigidity.

Fusion, however, has some undesirable side effects. One apparent sideeffect is the immobilization of a portion of the spine. Furthermore,although fusion may result in a strengthened portion of the spine, italso has been linked to more rapid degeneration and even hyper-mobilityand collapse of spinal motion segments that are adjacent to the portionof the spine being fused, reducing or eliminating the ability of suchspinal joints to move in a more normal relation to one another. Incertain instances, fusion has also failed to provide pain relief.

An alternative to fusion and the use of more rigid longitudinalconnecting members or other rigid structure has been a “soft” or“dynamic” stabilization approach in which a flexible loop-, S-, C- orU-shaped member or a coil-like and/or a spring-like member is utilizedas an elastic longitudinal connecting member fixed between a pair ofpedicle screws in an attempt to create, as much as possible, a normalloading pattern between the vertebrae in flexion, extension,distraction, compression, side bending and torsion. Problems may arisewith such devices, however, including soft tissue ingrowth withscarring, lack of adequate spinal support and lack of fatigue strengthor endurance limit. Fatigue strength has been defined as the repeatedloading and unloading of a specific stress on a material structure untilit fails. Fatigue strength can be tensile or distraction, compression,shear, torsion, bending, or a combination of these.

Another type of soft or dynamic system known in the art includes boneanchors connected by flexible cords or strands, typically made from asynthetic material. Such a cord or strand may be threaded throughcannulated spacers that are disposed between adjacent bone anchors whensuch a cord or strand is implanted, tensioned and attached to the boneanchors. The spacers typically span the distance between bone anchors,providing limits on the bending movement of the cord or strand and thusstrengthening and supporting the overall system. Such cord orstrand-type systems require specialized bone anchors and tooling fortensioning and holding the chord or strand in the bone anchors. Althoughflexible, the cords or strands utilized in such systems do not allow forelastic distraction or stretchability of the system once implantedbecause the cord or strand must be stretched or pulled to maximumtension in order to provide a stable, supportive system.

The complex dynamic conditions associated with spinal movement thereforeprovide quite a challenge for the design of elongate elasticlongitudinal connecting members that exhibit an adequate fatiguestrength to provide stabilization and protected motion of the spine,without fusion, and allow for some natural movement of the portion ofthe spine being reinforced and supported by the elongate elastic orflexible connecting member. A further challenge are situations in whicha portion or length of the spine requires a more rigid stabilization,possibly including fusion, while another portion or length may be bettersupported by a more dynamic system that allows for protected segmentalspinal movement.

SUMMARY OF THE INVENTION

Longitudinal connecting member assemblies according to the invention foruse between at least two bone anchors provide dynamic, protected motionof the spine and may be extended to provide additional dynamic sectionsor more rigid support along an adjacent length of the spine, withfusion, if desired. A longitudinal connecting member assembly accordingto the invention has an inner integral core or bar, a portion thereofhaving a slit. The slit is preferably helical. An outer sleeve or spacersurrounds the slitted portion of the core and is located entirelyoutside of a periphery of the slitted core or bar. In a preferredembodiment, the sleeve extends between a pair of adjacent bone anchorsand has a cylindrical cross-sectional shape. The slitted core and outersleeve cooperate dynamically, both features having some flexibility,with the outer sleeve primarily protecting and limiting flexing movementof the inner core. The outer sleeve may include a grooved portion thatmay be compressed upon installation between two bone anchors. Ascompared to dynamic systems that include flexible cords and spacers,embodiments according to the present invention advantageously allow forelastic distraction, elongation or stretchability of the connectingmember assembly.

A variety of embodiments according to the invention are possible. Forexample, the inner core may extend between three or more bone anchorswith some or all of the sections that are located between bone anchorshaving a slit and cooperating sleeve. Alternatively some of the sectionsmay be of a more rigid construction and not include slits and sleeves.

OBJECTS AND ADVANTAGES OF THE INVENTION

Therefore, it is an object of the present invention to overcome one ormore of the problems with bone attachment assemblies described above. Anobject of the invention is to provide dynamic medical implantstabilization assemblies having longitudinal connecting members thatinclude an integral inner core having a flexible portion that allows forbending, torsion, compression and distraction of the assembly. Anotherobject of the invention is to provide such an assembly wherein theflexible portion is insertable into a protective outer sleeve. A furtherobject of the invention is to provide such an assembly wherein the outersleeve is compressed upon installation, without having to directlytension the inner core, by compressing the bone anchors toward oneanother. A further object of the invention is to provide dynamic medicalimplant longitudinal connecting members that may be utilized with avariety of bone screws, hooks and other bone anchors. Another object ofthe invention is to provide a more rigid or solid connecting memberportion or segment, if desired, such as a solid rod portion beingintegral with and adjacent to the core having the flexible portion.Additionally, it is an object of the invention to provide a lightweight,reduced volume, low profile assembly including at least two bone anchorsand a longitudinal connecting member therebetween. Furthermore, it is anobject of the invention to provide apparatus and methods that are easyto use and especially adapted for the intended use thereof and whereinthe apparatus are comparatively inexpensive to make and suitable foruse.

Other objects and advantages of this invention will become apparent fromthe following description taken in conjunction with the accompanyingdrawings wherein are set forth, by way of illustration and example,certain embodiments of this invention.

The drawings constitute a part of this specification and includeexemplary embodiments of the present invention and illustrate variousobjects and features thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded front elevational view of a dynamic fixationconnecting member assembly according to the invention including an innercore with a helical slit and an outer sleeve.

FIG. 2 is a front elevational view of a dynamic fixation assemblyaccording to the invention including the connecting member assembly ofFIG. 1 and two bone screws.

FIG. 3 is an enlarged and partial front elevational view of a portion ofthe inner core of FIG. 1.

FIG. 4 is an enlarged and partial cross-sectional view taken along theline 4-4 of FIG. 3.

FIG. 5 is an enlarged cross-sectional view of the inner core taken alongthe line 5-5 of FIG. 1.

FIG. 6 is an enlarged cross-sectional view of the outer sleeve takenalong the line 6-6 of FIG. 1.

FIG. 7 is an exploded perspective view of the assembly of FIG. 2 showingthe dynamic fixation connecting member, the two bone screws and a pairof closure structures.

FIG. 8 is a perspective view of the assembly of FIG. 7 shown fullyassembled.

FIG. 9 is an enlarged cross-sectional view taken along the line 9-9 ofFIG. 8.

FIG. 10 is a front elevational view of a second embodiment of an innercore according to the invention having a slitted portion and a solidportion.

FIG. 11 is a front elevational view of a second longitudinal connectingmember assembly according to the invention having the inner core of FIG.10, an outer sleeve cooperating with the slitted portion and three bonescrews.

FIG. 12 is a front elevational view of a third embodiment of an innercore according to the invention having a pair of slitted portions.

FIG. 13 is a front elevational view of a third longitudinal connectingmember assembly according to the invention having the inner core of FIG.12, a pair of outer sleeves cooperating with the pair of slittedportions and three bone screws.

FIG. 14 is a front elevational view of a fourth embodiment of an innercore according to the invention having a pair of slitted portions and asolid portion.

FIG. 15 is a front elevational view of a fourth longitudinal connectingmember assembly according to the invention having the inner core of FIG.14, a pair of outer sleeves cooperating with the pair of slittedportions and four bone screws.

DETAILED DESCRIPTION OF THE INVENTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention, which may be embodied in variousforms. Therefore, specific structural and functional details disclosedherein are not to be interpreted as limiting, but merely as a basis forthe claims and as a representative basis for teaching one skilled in theart to variously employ the present invention in virtually anyappropriately detailed structure. It is also noted that any reference tothe words top, bottom, up and down, and the like, in this applicationrefers to the alignment shown in the various drawings, as well as thenormal connotations applied to such devices, and is not intended torestrict positioning of the connecting member assemblies of theapplication and cooperating bone anchors in actual use.

With reference to FIGS. 1-9, the reference numeral 1 generallydesignates a non-fusion dynamic stabilization longitudinal connectingmember assembly according to the present invention. The connectingmember assembly 1 includes an inner core 8 and an outer sleeve or spacer10. The inner core 8 is elongate, either linear or curvilinear, having acentral longitudinal axis A and also including a first end portion orsection 16 extending along the axis A, an opposite second end portion orsection 18 and a mid-portion or section 20 having a helical slit 22. Theinner core 8 is receivable in the flexible outer sleeve 10, with thesleeve 10 ultimately surrounding the slitted mid-portion 20 as will bedescribed more fully below. The dynamic connecting member assembly 1cooperates with at least a pair of bone anchors, such as the polyaxialbone screws, generally 25 and cooperating closure structures 27 shown inthe drawings, the assembly 1 being captured and fixed in place at theend portions 16 and 18 by cooperation between the bone screws 25 and theclosure structures 27. The sleeve 10 is sized and shaped to fit betweenpairs of bone screws 25 or other bone anchors, cooperating with theinner core 8 to support adjacent vertebrae. The sleeve 10 can be of anycross-sectional shape and can be cut to fit any needed length.

Because the end portions 16 and 18 are substantially solid and, in thisillustrated embodiment, cylindrical, the connecting member assembly 1may be used with a wide variety of bone anchors already available forcooperation with rigid rods including fixed, monoaxial bone screws,hinged bone screws, polyaxial bone screws, and bone hooks and the like,with or without compression inserts, that may in turn cooperate with avariety of closure structures having threads, flanges, or otherstructure for fixing the closure structure to the bone anchor, and mayinclude other features, for example, break-off tops and inner setscrews. The bone anchors, closure structures and the connecting memberassembly 1 are then operably incorporated in an overall spinal implantsystem for correcting degenerative conditions, deformities,instabilities, injuries, or defects (congenital, developmental) to thespinal column of a patient. The end portions 16 and 18 can be of anylength and the helical slit section can also vary in length.

The illustrated polyaxial bone screw 25 includes a shank 30 forinsertion into a vertebra (not shown), the shank 30 being pivotallyattached to an open receiver or head 31. The shank 30 includes athreaded outer surface and a central cannula or through-bore 32 disposedalong an axis of rotation of the shank, the through-bore 32 extendingbetween a top surface 33 and a bottom surface 34 of the shank 30. Thebore 32 provides a passage through the shank interior for a length ofwire or pin inserted into the vertebra prior to the insertion of theshank 30, the wire or pin providing a guide for insertion of the shank30 into the vertebra.

The receiver 31 has a pair of spaced and generally parallel arms 35 thatform an open generally U-shaped channel 37 therebetween that is open atdistal ends of the arms 35. The arms 35 each include radially inward orinterior surfaces 40 that have a discontinuous guide and advancementstructure mateable with cooperating structure on the closure structure27. In the illustrated embodiment, the guide and advancement structureis a partial helically wound flangeform configured to mate underrotation with a similar structure on the closure structure 27. However,it is foreseen that the guide and advancement structure couldalternatively be a buttress thread, a square thread, a reverse anglethread or other thread like or non-thread like helically woundadvancement structures for operably guiding under rotation and advancingthe closure structure 27 downward between the receiver arms 35 andhaving such a nature as to resist splaying of the arms 35 when theclosure 27 is advanced into the U-shaped channel 37.

Each of the arms 35 also includes a V-shaped or undercut tool engagementgroove 41 formed on a substantially planar outer surface thereof whichmay be used for holding the receiver 31 with a holding tool (not shown)having projections that are received within the grooves 41 duringimplantation of the shank 30 into the vertebra (not shown). The grooves41 may also cooperate with a holding tool during bone screw assembly andduring subsequent installation of the connecting member assembly 1 andthe closure structure 27. It is foreseen that tool receiving grooves orapertures may be configured in a variety of shapes and sizes and bedisposed at other locations on the receiver arms 35.

The shank 30 and the receiver 31 may be attached in a variety of ways.For example, a spline capture connection as described in U.S. Pat. No.6,716,214, and incorporated by reference herein, is shown in the drawingfigures wherein the bone screw shank 30 includes a capture structure 42mateable with a retaining structure 44 disposed within the receiver. Theretaining structure 44 includes a partially spherical surface that isslidingly mateable with a cooperating inner surface of the receiver 31,allowing for a wide range of pivotal movement between the shank 30 andthe receiver 31. Polyaxial bone screws with other types of captureconnections may also be used according to the invention, including butnot limited to, threaded connections, frictional connections utilizingfrusto-conical or polyhedral capture structures, integral top ordownloadable shanks, and the like. Also, as indicated above, polyaxialand other bone screws for use with connecting members of the inventionmay have bone screw shanks that attach directly to the connecting memberor may include compression members or inserts that cooperate with thebone screw shank, receiver and closure structure to secure theconnecting member assembly to the bone screw and/or fix the bone screwshank at a desired angle with respect to the bone screw receiver thatholds the longitudinal connecting member assembly. Furthermore, althoughthe closure structure 27 of the present invention is illustrated withthe polyaxial bone screw 25 having an open receiver or head 31, itforeseen that a variety of closure structure may be used in conjunctionwith any type of medical implant having an open or closed head,including monoaxial bone screws, hinged bone screws, hooks and the likeused in spinal surgery.

To provide a biologically active interface with the bone, the threadedshank 30 may be coated, perforated, made porous or otherwise treated.The treatment may include, but is not limited to a plasma spray coatingor other type of coating of a metal or, for example, a calciumphosphate; or a roughening, perforation or indentation in the shanksurface, such as by sputtering, sand blasting or acid etching, thatallows for bony ingrowth or ongrowth. Certain metal coatings act as ascaffold for bone ingrowth. Bio-ceramic calcium phosphate coatingsinclude, but are not limited to: alpha-tri-calcium phosphate andbeta-tri-calcium phosphate (Ca₃ (PO₄)₂, tetra-calcium phosphate(Ca₄P₂O₉), amorphous calcium phosphate and hydroxyapatite(Ca₁₀(PO₄)₆(OH)₂). Coating with hydroxyapatite, for example, isdesirable as hydroxyapatite is chemically similar to bone with respectto mineral content and has been identified as being bioactive and thusnot only supportive of bone ingrowth, but actively taking part in bonebonding.

The longitudinal connecting member assembly 1 illustrated in FIGS. 1-9is elongate, with the inner core 8 being made from metal, metal alloysor other suitable materials, including plastic polymers such aspolyetheretherketone (PEEK), ultra-high-molecular weight-polyethylene(UHMWP), polyurethanes and composites. The outer sleeve or spacer 10 maybe made of a variety of materials including metals, plastics andcomposites. The illustrated sleeve 10 is made from a plastic, such as athermoplastic elastomer, for example, polycarbonate-urethane. In orderto reduce the production of micro wear debris, that in turn may causeinflammation, it is desirable to make the inner core 8 from a differentmaterial than the sleeve 10. Additionally or alternatively, in order toresult in adequate hardness and low or no wear debris, the sleeve 10inner surfaces and cooperating core 8 outer surfaces may be coated withan ultra thin, ultra hard, ultra slick and ultra smooth coating, such asmay be obtained from ion bonding techniques and/or other gas or chemicaltreatments.

Specifically, with the exception of the slitted mid portion 20, theillustrated core 8 is a substantially solid, smooth and uniform cylinderor rod having an outer cylindrical surface 50 and a circularcross-section. It is foreseen that in some embodiments, the core 8 maybe substantially hollow, having a bore extending along the axis A all orpart of an entire length of the core 8. The illustrated core 8 has anend 52 and an opposite end 54, with the solid end portion 16 terminatingat the end 52 and the solid end portion 18 terminating at the end 54.The portions 16 and 18 are each sized and shaped to be received in theU-shaped channel 37 of a bone screw assembly 25 with the mid-portion 20sized and shaped to extend between cooperating bone screws 25. It isforeseen that the core could be non-cylindrical in shape and incross-section and that it can be cut to length to fit any clinicalapplication.

With particular reference to FIGS. 3-5, the mid-portion 20 includes thehelical slit 22 that is formed in and extends from the outer surface orperiphery 50 toward the axis A. In the illustrated embodiment, a processof forming the helical slit 22 creates an aperture, inner space or bore57 that extends along the axis A along a length L of the slit 22. Inembodiments wherein the core 8 already has a through bore extendingalong the axis A, the helical slit extends through the outer surface 50and an inner surface that defines such bore. The slit 22 disposed inpart or all of the mid-portion 20, results in the mid-portion beingcoil- or spring-like in nature. Thus, when the core 8 is fixed to bonescrews 25 at the end portions 16 and 18 thereof, the slitted mid-portion20 provides relief (e.g., shock absorption) and limited movement withrespect to flexion, extension, torsion, distraction and compressiveforces placed on the assembly 1.

The sleeve 10 advantageously cooperates with the core helical slit 22and is slidable thereon, providing limitation and protection of movementof the core 8 at the slit 22. The sleeve 10 also protects patient bodytissue from damage that might otherwise occur in the vicinity of thehelical slit 22. The sleeve 10 prevents soft tissue ingrowth into theslit 22 that could hinder the function of the slit 22. The sleeve 10 issized and shaped for substantially even and precise alignment andsubstantial compressive contact between flat end surfaces 58 a and 58 bof the sleeve 10 and cooperating flat side surfaces 59 of the receivers31. Furthermore, as will be discussed in greater detail below, when thesleeve is implanted, and the closure structures 27 are tightened, thetools utilized to implant the assembly 1 and/or the bone screws 27 aremanipulated so as to axially compress the sleeve 10, now substantiallycoaxial with the core 8 axis A, between facing side surfaces 59 ofadjacent receivers 31. Such pre-compression after installation resultsin some tension and distraction of the slitted mid-portion 20 of thecore 8 when the implantation tools are removed from the bone screws 25,as the sleeve surfaces 58 a and 58 b then press against the facing bonescrew surfaces 59, but the core 8 is otherwise fixed with respect toeach of the bone screws 27 within the receiver channels 37. Such dynamictension/compression relationship between the sleeve 10 and the slittedcore 8 provides further strength and stability to the overall assemblyand also allows for the entire connecting member assembly 1 to elongate,if needed, in response to spinal movement. The increased stability andstrength of the assembly advantageously allows for use of a smaller,more compact, reduced volume, lower profile longitudinal connectingmember assembly 1 and cooperating bone anchors than, for example,flexible cord and spacer type longitudinal connecting member assemblies.Also this type of assembly using a flexible non-cord like member allowsthe use of any type of bone anchor, polyaxial or not.

In the embodiment shown, the sleeve 10 is also substantially cylindricalwith an external substantially cylindrical surface 60 and an internalsubstantially cylindrical and smooth surface 62. The surface 62 definesa bore 66 with a circular cross section, the bore 66 extending throughthe sleeve 10. In the illustrated embodiment, the sleeve 10 furtherincludes a plurality of compression grooves 68. Sleeves according to theinvention may include one, none or any desired number of grooves 68.Each of the illustrated grooves 68 is substantially uniform and circularin cross-section as illustrated in FIG. 6, being formed in the externalsurface 60 and extending radially toward the internal surface 62. Theinternal surface 62 is of a slightly greater diameter than an outerdiameter of the cylindrical surface 50 of the core 8, allowing foraxially directed sliding movement of the sleeve 10 with respect to thecore 8. When the cylindrical core 8 is inserted in the sleeve 10, thesleeve 10 completely surrounds the helical slit 22. It is noted that inaddition to limiting the bendability of the core 8 and thus providingstrength and stability to the assembly 1, the sleeve 10 also keeps scartissue from growing into the core 8 through the helical slit 22, thuseliminating the need for a sheath-like structure to be placed, adheredor otherwise applied to the core 8.

The core 8 may be sized and made from such materials as to provide for arelatively more rigid assembly 1 or a relatively more flexible assembly1 with respect to flex or bendability along the assembly 1. Suchflexibility therefore may be varied by changing the outer diameter ofthe core 8 and thus likewise changing the inner diametric size of thesleeve 10. Also, since the distance between the bone screw assemblyreceivers or heads can vary, the core 8 may need to be more or lessstiff. The pitch of the helical slit 22 may also be varied to provide amore or less flexible core and the shock absorption desired. Forexample, it is noted that increasing the pitch (i.e., forming a moreacute angle between the slant of the slit 22 with respect to the axis Aresults in a stiffer assembly with respect to bending and axialdisplacements. Furthermore, a benefit of increasing pitch is a lesseningof impact loading between the surfaces defining the helical slit 22,thus dampening the jolts of an impact and improving shock absorption.Again the length of the slitted section can vary.

With reference to FIGS. 7-9, the closure structure 27 can be any of avariety of different types of closure structures for use in conjunctionwith the present invention with suitable mating structure on theinterior surface 40 of the upstanding arms 35 of the receiver 31. Theillustrated closure structure 27 is rotatable between the spaced arms35, but could be, for example, a slide-in closure structure or a ninetydegree twist-in closure with opposed flange-like or wedge-likeprojections. The illustrated closure structure 27 is substantiallycylindrical and includes an outer helically wound guide and advancementstructure in the form of a flange form 76 that operably joins with theguide and advancement structure disposed on the interior 40 of the arms35. The flange form 76 utilized in accordance with the present inventionmay take a variety of forms, including those described in Applicant'sU.S. Pat. No. 6,726,689, which is incorporated herein by reference. Itis also foreseen that according to the invention the closure structureguide and advancement structure could alternatively be a buttressthread, a square thread, a reverse angle thread or other thread like ornon-thread like helically wound advancement structure for operablyguiding under rotation and advancing the closure structure 27 downwardbetween the arms 35 and having such a nature as to resist splaying ofthe arms 35 when the closure structure 27 is advanced into the U-shapedchannel 37.

The illustrated closure structure 27 includes a lower surface 78 that issubstantially planar and includes a point 80 and a rim 82 protrudingtherefrom for engaging the core 8 outer cylindrical surface at thenon-slitted end portion 16 or 18. The closure structure 27 has a topsurface 84 with an internal drive in the form of an aperture 86,illustrated as a star-shaped internal drive, for example, sold under thetrademark TORX. A driving tool (not shown) sized and shaped forengagement with the internal drive 86 is used for both rotatableengagement and, if needed, disengagement of the closure 27 from the arms35. Although a star-shaped internal drive 86 is shown in the drawings,the tool engagement structure may take a variety of forms and mayinclude, but is not limited to, a hex shape or other features orapertures, such as slotted, tri-wing, spanner, two or more apertures ofvarious shapes, and the like. It is also foreseen that the closurestructure 27 may alternatively include a break-off head designed toallow such a head to break from a base of the closure at a preselectedtorque, for example, 70 to 140 inch pounds. Such a closure structurewould also include a base having an internal drive to be used forclosure removal.

In use, at least two bone anchor assemblies 25 are implanted intovertebrae for use with the longitudinal connecting member assembly 1.Each vertebra may be pre-drilled to minimize stressing the bone whenscrews are used. Furthermore, if and when a cannulated bone screw shankis utilized, each vertebra could have a guide wire or pin (not shown)inserted therein that is shaped for the bone screw cannula 32 of thebone screw shank 30 and provides a guide for the placement and angle ofthe shank 30 with respect to the cooperating vertebra. A further taphole may be made and the shank 30 is then driven into the vertebra byrotation of a driving tool (not shown) that engages a driving featurenear the top 33 of the shank 30 illustrated as a hex-shaped head. It isforeseen that the screws 25 and the longitudinal connecting member 1 canbe inserted in a percutaneous or minimally invasive surgical manner.

With particular reference to FIG. 1, the longitudinal connecting memberassembly 1 is assembled by inserting the core 8 into the bore 66 definedby the inner cylindrical surface 62 of the outer sleeve 10 after boththe core 8 and the sleeve 10 have been cut to length. The end 54 of thecore 8 is placed into the bore 66 at the surface 58 a and the sleeve 10is moved toward the end portion 16 until the sleeve 10 is positionedbetween the end portions 16 and 18 and is disposed about the mid-portion20, thus covering or encompassing the helical slit 22. It is noted thatthe core 8 and the sleeve 10 may also be assembled in other ways, forexample, by inserting the end 52 of the core 8 into the sleeve 10 at theend surface 58 b. Furthermore, alignment of the slit 22 with respect tothe grooves 68 along the axis A as shown, for example, in FIG. 2 isapproximate and not intended to limit the relative position or locationof the slit 22 with respect to the grooves 68 or the slit with respectto the pair of receivers 31. Such positioning may be determined, forexample, in relation to a degree of overall flexibility desired for theassembly 1.

The connecting member assembly 1 is eventually positioned in an open orpercutaneous manner in cooperation with the at least two bone anchors orscrews 25 with the sleeve 10 disposed between the two bone screws 25 andthe end portions 16 and 18 each within the U-shaped channels 37 of thetwo bone screws 25. Again, the end portions 16 and 18 could extend toother bone anchors. A closure structure 27 is then inserted into andadvanced between the arms 35 of each of the bone anchor screws 25. Theclosure structure 27 is rotated, using a tool engaged with the innerdrive 86 until a selected pressure is reached at which point the core 8is urged toward, but not completely seated in the channel 37. Forexample, about 80 to about 120 inch pounds pressure may be required forfixing the bone screw shank 30 with respect to the receiver 31.

Downward movement of the closure structure 27 into the channel 37presses a respective end portion 16 or 18 downward into engagement witha top 33 or other upper portion of the respective bone screw shank 30,pressing the respective retaining structure 44 into engagement with therespective receiver 31, thus setting an angle of articulation of therespective shank 30 with respect to the respective receiver 31, clampingthe shank 30 into a fixed position with respect to the receiver 31. Thereceiver 31, the shank 30 and the retaining structure 44 cooperate insuch a manner that the receiver 31 and the shank 30 can be secured atany of a plurality of angles, articulations or rotational alignmentsrelative to one another and within a selected range of angles both fromside to side and from front to rear, to enable flexible or articulatedengagement of the receiver 31 with the shank 30 until both are locked orfixed relative to each other. Again it is also possible to use fixed ormonoaxial screws with the invention, as described below.

Alternatively, it is foreseen that the capture of the connecting memberassembly 1 by bone screws or other bone anchors and cooperating closurestructures could further involve the use of an upper and/or a lowercompression member or insert. Furthermore, the assembly 1 may cooperatewith an open receiver that is integral or fixed in position with respectto a bone screw shank or bone hook, or with a receiver having limitedangular movement with respect to the shank, such as a hinged connection,also with or without other compression members or inserts for fixing theassembly 1, the receiver and/or the bone anchor in a desired position ororientation with respect to the cooperating vertebrae.

As indicated previously herein, as the closure structures 27 are rotatedand then tightened against the end portions 16 and 18 within a pair ofspaced bone screws 25, such bone screws 25 may be pressed toward oneanother, thereby compressing and pre-loading the sleeve 10. When theinsertion and tightening tools are removed, the resilient sleeve 10,pressing against facing surfaces 59 of the cooperating bone screwreceivers 31, stretches and tensions the mid-portion 20 of the core 8 atthe helical slit 22. The assembly 1 is thus substantially dynamicallyloaded and oriented relative to the cooperating vertebra, providingrelief (e.g., shock absorption) and protected movement with respect toflexion, extension, torsional and distraction and compressive forcesplaced on the assembly 1 and the two connected bone screws 25. Again,the helical slit 22 allows the core 8 to twist or turn, providing relieffor torsional stresses. The sleeve 10 can also limit such torsionalmovement as well as bending movement of the core 8, providing spinalsupport. Furthermore, because the sleeve 10 is compressed duringinstallation, the sleeve advantageously allows for some protectedextension or distraction of both the core 8 and the sleeve 10 as well ascompression of the assembly 1 in cooperation with the core 8.

If removal of the assembly 1 from any of the bone screw assemblies 25 isnecessary, or if it is desired to release the assembly 1 at a particularlocation, disassembly is accomplished by using the driving tool (notshown) with a star-shaped driving formation on the closure structure 27internal drive 86 to rotate and remove the closure structure 27 from thereceiver 31. Disassembly is then accomplished in reverse order to theprocedure described previously herein for assembly.

Eventually, if the spine requires more rigid support, the connectingmember assembly 1 according to the invention may be removed and replacedwith another longitudinal connecting member, such as a solid rod, havingthe same diameter as the inner core 8 end portions 16 and 18, utilizingthe same receivers 31 and closure structures 27. Alternatively, if lesssupport is eventually required, a less rigid, more flexible assembly,for example, an assembly 1 made of a more flexible material or anassembly 1 having a slit of different length and/or pitch, but with endportions having the same diameter as the inner core 8 end portions 16and 18, may replace the assembly 1, also utilizing the same bone screws25.

With reference to FIGS. 10 and 11, an alternative longitudinalconnecting member assembly according to the invention, generally 101includes an inner core 108 and an outer sleeve 110. The outer sleeve 110is the same or substantially similar to the sleeve 10 previouslydescribed herein. The assembly 101 is shown attached to three bone screwassemblies 25, previously described herein, each bone screw assemblyhaving a shank 30 and a receiver 31, also previously described herein.Although not shown, each bone screw assembly 25 further includes aclosure structure 27, also previously described herein. As with theassembly 1, the assembly 101 readily cooperates with a wide variety ofbone anchors and closures, also as previously described herein.

The connecting member assembly 101 is sized and shaped to attach to atleast three bone screw assemblies 25, to provide a flexible dynamicstabilization length or segment 124 where the core 108 has a slit 122and cooperates with the sleeve 110. The core length or segment 124 andthe slit 122 are similar or nearly identical to the core 8 and sleeve10, respectively, previously described herein. However, the segment 124is integral or otherwise fixed to a more rigid length or segment 126that is of solid construction and may be used in conjunction with spinalfusion along such length. The flexible length 124 that includes the slit122 is disposed between the rigid length 126 and another shorter rigidlength or portion 128 sized and shaped to be received by the third bonescrew assembly 25. The sleeve 110 includes grooves 168 the same orsubstantially similar to the grooves 68 previously described herein withrespect to the sleeve 10. Also, in the illustrated embodiment theportion 128 is substantially similar or identical to the end portion 16previously described herein with respect to the core 8. It is noted thatthe portion 128 may also be elongate of any length, similar to thelength 126, for cooperating with more than one bone anchor or bone screwassembly 25. Thus, an assembly 101 according to the invention may beused to provide protected movement of the spine along the segment 124,spinal fusion along the length 126 and spinal fusion on a lengthopposite the length 128, if the portion 128 is of sufficient length toattach to another bone screw assembly 25. It is noted that a portion orportions of the assembly 101 can be straight or curved, pre-bent orcurvilinear.

In the illustrated embodiment, the portions or segments 124, 126 and 128are integral and substantially uniform along a central longitudinal axisB thereof, and are cylindrical. The segments 124, 126 and 128 are alsoof solid construction with the exception of the portion of the segment124 that has the helical slit 122. As indicated above, the helical slit122 is similar or identical to the helical slit 22 previously describedherein, having features and cross-sections as shown in FIGS. 3, 4 and 5.

In use, the assembly 101 is implanted in a manner substantially similarto that previously described herein with respect to the assembly 1. Thesegment 126 is ultimately located near a portion of the spine requiringmore rigid support while the segment 124 and cooperating sleeve 110 arelocated near a portion of the spine requiring less support. If desired,during tightening of the closure structures 27 against the core 108, thesleeve 110 is compressed between facing bone screw receivers 31 aspreviously described herein with respect to the sleeve 10.

It is noted that an advantageous connecting member 101 according to theinvention includes a rigid length or segment 126 made from a metal alloythat is elongate and intended for fusion along a major portion orsection of the spine, for example, the rigid length 126 may be sized toextend from the sacrum to the thoracic spinal segment T10. Such anelongate portion or segment 126 is thus connectable to a plurality ofbone anchors along the spine. Such a connecting member further includesa dynamic section 124 having a slit 122 and spacer or sleeve 110 that issized for placement, for example, between T9 and T8. Such an embodimentis believed to minimize rapid degeneration and compressive fracturesthat tend to occur near ends of such elongate connecting memberassemblies.

With reference to FIGS. 12 and 13, another alternative longitudinalconnecting member assembly according to the invention, generally 201includes an inner core 208 and two outer sleeves 210 a and 210 b. Theouter sleeves 210 a and 210 b are the same or substantially similar tothe sleeve 10 previously described herein. The assembly 201 is shownattached to three bone screw assemblies 25, previously described herein,each bone screw assembly having a shank 30 and a receiver 31, alsopreviously described herein. Although not shown, each bone screwassembly 25 further includes a closure structure 27, also previouslydescribed herein. As with the assemblies 1 and 101, the assembly 201readily cooperates with a wide variety of bone anchors and closures,also as previously described herein.

The connecting member assembly 201 is sized and shaped to attach to atleast three bone screw assemblies 25, to provide two flexible dynamicstabilization lengths or segments 224 a and 224 b where the core 108 hasrespective slits 222 a and 222 b that cooperate with the respectivesleeves 210 a and 210 b. The core lengths or segments 224 a and 224 band the slits 222 a and 222 b are similar or nearly identical to thecore 8 and sleeve 10, respectively, previously described herein. Theillustrated segment 224 a is integral with the segment 224 b. Theflexible length 224 a that includes the slit 222 a is integral orotherwise fixed to a rigid length 226. The flexible length 224 b thatincludes the slit 222 b is integral or otherwise fixed to a rigid length228. In the illustrated embodiment, the lengths 226 and 228 arerelatively short in length, being sized and shaped to be received by areceiver 31 of one of the bone screw assemblies 25. The sleeves 210 aand 210 b each include respective grooves 268 a and 268 b that are thesame or substantially similar to the grooves 68 previously describedherein with respect to the sleeve 10. Also, in the illustratedembodiment, the portions 226 and 228 are substantially similar oridentical to the end portions 16 and 18 previously described herein withrespect to the core 8. It is noted that the portions 226 and 228 mayalso be elongate, similar to the length 126 of the core 108, forcooperating with more than one bone screw assembly 25.

Thus the assembly 201 according to the invention is used to provideprotected movement of the spine along both the segments 224 a and 225 b.In the illustrated embodiment, the portions or segments 224 a, 224 b,226 and 228 are integral and substantially uniform along a centrallongitudinal axis C thereof, and are cylindrical. The segments 224 a,224 b, 226 and 228 are also of solid construction with the exception ofthe portions of the segments 224 a and 224 b that have the respectivehelical slits 222 a and 222 b. As indicated above, the helical slits 222a and 222 b are substantially similar or identical to the helical slit22 previously described herein, having features and cross-sections asshown in FIGS. 3, 4 and 5.

In use, the assembly 201 is implanted in a manner substantially similarto that previously described herein with respect to the assembly 1. Aswith the assembly 1, if desired, during tightening of the closurestructures 27 against the core 208, one or both of the sleeves 210 a and210 b may be compressed between facing bone screw receivers 31 aspreviously described herein with respect to the sleeve 10.

With reference to FIGS. 14 and 15, another alternative longitudinalconnecting member assembly according to the invention, generally 301includes an inner core 308 and two outer sleeves 310 a and 310 b. Theouter sleeves 310 a and 310 b are the same or substantially similar tothe sleeve 10 previously described herein. The assembly 301 is shownattached to four bone screw assemblies 25, previously described herein,each bone screw assembly having a shank 30 and a receiver 31, alsopreviously described herein. Although not shown, each bone screwassembly 25 further includes a closure structure 27, also previouslydescribed herein. As with the assemblies 1, 101 and 201, the assembly301 readily cooperates with a wide variety of bone anchors and closures,also as previously described herein.

The connecting member assembly 301 is sized and shaped to attach to atleast four bone screw assemblies 25, to provide two flexible dynamicstabilization lengths or segments 324 a and 324 b and one rigid length328. At the segments 324 a and 324 b, respective slits 322 a and 322 bcooperate with the respective sleeves 310 a and 310 b. The core lengthsor segments 324 a and 324 b and the slits 322 a and 322 b are similar ornearly identical to the core 8 and sleeve 10, respectively, previouslydescribed herein. However, the segment 324 a is integral with thesegment 324 b and the segment 324 b is integral with the rigid length orsegment 328. The flexible length 324 a that includes the slit 322 a isalso integral or otherwise fixed to a shorter rigid length 326. In theillustrated embodiment, the length 326 is sized and shaped to bereceived by a receiver 31 of one of the bone screw assemblies 25 whilethe length 328 is elongate, of solid construction and sized to cooperatewith at least two bone screw assemblies 25. The length 328 may be usedin conjunction with spinal fusion. The sleeves 310 a and 310 b eachinclude respective grooves 368 a and 368 b that are the same orsubstantially similar to the grooves 68 previously described herein withrespect to the sleeve 10. Also, in the illustrated embodiment, theportion 326 is substantially similar or identical to the end portion 16previously described herein with respect to the core 8. It is noted thatthe portion 326 may also be elongate, similar to the length 328, forcooperating with more than one bone screw assembly 25.

Thus the assembly 301 according to the invention is used to provideprotected movement of the spine along both the segments 324 a and 325 band rigid support along the length 328. In the illustrated embodiment,the portions or segments 324 a, 324 b, 326 and 328 are integral andsubstantially uniform along a central longitudinal axis D thereof, andare cylindrical. The segments 324 a, 324 b, 326 and 328 are also ofsolid construction with the exception of the portions of the segments324 a and 324 b that have the respective helical slits 322 a and 322 b.As indicated above, the helical slits 322 a and 322 b are substantiallysimilar or identical to the helical slit 22 previously described herein,having features and cross-sections as shown in FIGS. 3, 4 and 5.

In use, the assembly 301 is implanted in a manner substantially similarto that previously described herein with respect to the assembly 1. Aswith the assembly 1, if desired, during tightening of the closurestructures 27 against the core 308, one or both of the sleeves 310 a and310 b may be compressed between facing bone screw receivers 31 aspreviously described herein with respect to the sleeve 10.

It is to be understood that while certain forms of the present inventionhave been illustrated and described herein, it is not to be limited tothe specific forms or arrangement of parts described and shown.

1. In a medical implant assembly having at least two bone attachmentstructures, including a first and a second bone attachment structure,the first and second bone attachment structures cooperating with alongitudinal connecting member, the improvement wherein the longitudinalconnecting member comprises: a) an inner core having a periphery and aslit formed into a portion of the periphery, the core being integralalong an entire length of the connecting member and secured to the firstand second bone attachment structures; and b) an elasticallycompressible outer sleeve including opposed flat end surfaces adaptedfor flush engagement with a side surface of each of the first and secondbone attachment structures, and covering the slit of the inner core, thesleeve disposed outside of the periphery, allowing respective freedom ofmovement between the inner core and the outer sleeve, the sleevepositioned entirely between the first and second bone attachmentstructures so as to be axially compressed by the first and second boneattachment structures, so as to provide a dynamic tension-compressionrelationship between the axially compressed sleeve and the inner coreslitted portion.
 2. The improvement of claim 1 wherein the slit is ahelical slit disposed on a portion of the inner core and positionedbetween the first and second bone attachment structures.
 3. Theimprovement of claim 1 wherein the sleeve extends between and makescontact with the first and second bone attachment structures, whereinthe sleeve does not extend through the first and second bone attachmentstructures.
 4. The improvement of claim 3 wherein the sleeve iscompressed during installation.
 5. The improvement of claim 1 whereinthe core is cylindrical.
 6. The improvement of claim 1 wherein thesleeve has an external surface with at least one groove formed in thesurface.
 7. The improvement of claim 1 wherin the sleeve has acylindrical external surface with at least one and up to a plurality ofcompression grooves formed thereon.
 8. The improvement of claim 1wherein the inner core has a first longitudinal section and an integralsecond longitudinal section, the first longitudinal section having theslit, the first longitudinal section extending between the first andsecond bone attachment structures and the second longitudinal sectionextending between the second bone attachment structure and a third boneattachment structure.
 9. The improvement of claim 8 wherein the secondlongitudinal section has a second slit.
 10. The improvement of claim 8wherein the second longitudinal section is a solid rod.
 11. Theimprovement of claim 8 wherein the inner core member has a thirdlongitudinal section extending between the third bone attachmentstructure and a fourth bone attachment structure.
 12. In a medicalimplant assembly having at least first and second bone anchorscooperating with a longitudinal connecting member, the improvementwherein the connecting member comprises: a) an elongate bar of one-piececonstruction, the bar attachable to the first and second bone anchors,the bar having a slitted portion; and b) an elastically compressibleouter sleeve including opposed flat end surfaces adapted for flushengagement with a side surface of each of the first and second boneattachment structures, and surrounding the slitted portion and beingslidable with respect to the slitted portion, the sleeve beingpositioned entirely between the first and second bone anchors.
 13. Theimprovement of claim 12 wherein the bar is substantially solid.
 14. Theimprovement of claim 13 wherein the slitted portion is a substantiallyhelical slit formed in the substantially solid bar.
 15. The improvementof claim 12 wherein the bar is substantially cylindrical.
 16. Alongitudinal connecting member for cooperation with at least two boneanchors of a medical implant assembly, the assembly including a firstbone anchor and a second bone anchor, the member comprising: a) asubstantially solid bar of one-piece construction having first andsecond ends and a helical slit formed on a portion of the bar spacedfrom both the first and second ends; and b) a sleeve having a throughbore, the bar receivable in the bore and freely slidable with respect tothe sleeve, the sleeve being positioned over the bar portion having thehelical slit, the sleeve being positioned entirely between and incontact with the first and second bone anchors, wherein the sleeve iselastically compressible and has initial flush engagement with at leastone of the bone attachment structures when initially implanted.